Solar power receivers have been made in a number of different configurations. Pressurized (high pressure) and open (low pressure) solar power receivers have both been tested successfully in research facilities and pre-commercial demonstration plants have been built. Prior receivers that can generate hot pressurized air include tubular receivers and closed volumetric receivers.
Tubular receivers are termed indirectly-irradiated receivers and generally consist of multiple high temperature resistant metal alloy boiler tubes through which a pressurized working fluid is passed such as compressed air, water/steam, carbon dioxide or any other suitable working fluid.
On the other hand, closed volumetric receivers are regarded as directly-irradiated receivers. Closed volumetric receivers typically make use of a pressurized quartz window through which solar irradiation passes and strikes a porous absorber medium inside a pressurized chamber. Pressurized gas moves through the absorber medium and thus gains thermal energy while cooling down the absorber medium.
Open (low pressure) volumetric receivers are also generally directly irradiated receivers. In this instance ambient air, instead of pressurized gas, is drawn through an absorber medium that is exposed to concentrated solar radiation. A limitation of an open volumetric receiver is that it can, at the present state of technological development, only practically be used in a limited number of applications such as Rankine cycle for the production of electrical energy.
R. Buck et al. in an article entitled “Dual-receiver concept for solar towers” (Solar Energy 80 (2006) 1249-1254) describe a low pressure type of solar receiver in which evaporation is performed in directly irradiated absorber tubes, while feed water pre-heating and steam superheating is done in a heat exchanger fed with hot air from an open volumetric receiver. The entire arrangement operates on the Rankine cycle.
US Patent Publication No. US20110185742 to Heide et al proposes several combined cycle concentrating solar power plant layouts, featuring a separate heat transfer medium cycle around the receiver, a high temperature thermal energy storage system in this cycle, a heat exchanger to a Brayton cycle and a Rankine steam cycle, which has two heat sources. One of them is a solar boiler in which the high temperature medium generates steam and the other one is powered from the exhaust gases of the gas turbine.
US Patent Publication No. 2013/0207402 describes a combined cycle power plant with two different pressure levels on the gas side. It mentions air receivers at two different pressure levels and two different vertical locations. However, all of their receivers are pressurized and feed the gas turbines.
U.S. Pat. No. 8,312,703 to Aoyama et al proposes four different embodiments of a solar driven combined cycle plant. They feature pressurized air and steam superheating receivers wherein the steam is generated through the gas turbine exhaust gases. In some of the proposals, the air receiver is cooled by the superheated steam. One embodiment features an auxiliary fuel burner and one has only a pressurized air receiver. In the cases with two receivers, it is stated that in low part-load, the air-receiver is not used and the energy is concentrated on the steam receiver, which has a lower rating.
European Patent EP 2525051 to Aga et al describes a steam generating receiver and a separate receiver for charging a molten salt thermal energy storage system. During the discharge mode, energy for steam generation is provided by the molten salt by way of a heat exchanger. Focusing of heliostats on either one of the receivers located on one or several towers is mentioned.
It is known that a gas turbine operated by a high-pressure high-temperature working fluid operates most efficiently within rather limited ranges of thermal energy input by way of the pressurized working fluid. This being so, a balance needs to be considered when designing a gas turbine operated system in order to target a design efficiency. The solar heat source needs to be scaled to such a level that the gas turbine can operate for as much time as possible, while minimizing the necessity to defocus mirrors from the receiver.